Multi sensor radio frequency detection

ABSTRACT

Radio frequency motion sensors may be configured for operation in a common vicinity so as to reduce interference. In some versions, interference may be reduced by timing and/or frequency synchronization. In some versions, a master radio frequency motion sensor may transmit a first radio frequency (RF) signal. A slave radio frequency motion sensor may determine a second radio frequency signal which minimizes interference with the first RF frequency. In some versions, interference may be reduced with additional transmission adjustments such as pulse width reduction or frequency and/or timing dithering differences. In some versions, apparatus may be configured with multiple sensors in a configuration to emit the radio frequency signals in different directions to mitigate interference between emitted pulses from the radio frequency motion sensors.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of the filing dates of U.S.Provisional Patent Application No. 62/149,916 filed Apr. 20, 2015, andU.S. Provisional Patent Application No. 62/207,670 filed Aug. 20, 2015,the disclosures of which are hereby incorporated herein by reference.

FIELD OF THE TECHNOLOGY

The present technology relates to circuits and sensors for detection ofcharacteristics of moving objects and living subjects. Moreparticularly, it relates to such sensors for generating radio frequencyemissions, such as range gated pulses, motion sensing, with particularemphasis on improving sensor operation when in close proximity withsimilar sensors.

BACKGROUND OF THE TECHNOLOGY

Continuous wave (CW) Doppler radar motion sensors emit a continuous waveradio frequency (RF) carrier and mix the transmitted RF with the returnechoes to produce a difference frequency equal to the Doppler shiftproduced by a moving target. These sensors do not have a definite rangelimit (i.e., they can receive signals for both near and far objects,with the received signal being a function of radar cross section). Thiscan lead to false triggers i.e., motion artefact interference. They mayalso have an undesirably high sensitivity at close range that leads tofalse triggering.

A pulse Doppler motion sensor is described in U.S. Pat. No. 4,197,537 toFollen et al. A short pulse is transmitted and its echo is self-mixedwith the transmitted pulse. The pulse width defines the range-gatedregion. When the transmit pulse ends, mixing ends and target returnsarriving after the end of the transmit pulse are not mixed and arethereby gated out.

A Differential pulse Doppler motion sensor disclosed in U.S. Pat. No.5,966,090, “Differential Pulse Radar Motion Sensor,” to McEwan,alternately transmits two pulse widths. It then subtracts the Dopplerresponses from each width to produce a range gated Doppler sensingregion having a fairly constant response versus range.

Impulse radar, such as that described in U.S. Pat. No. 5,361,070,“Ultra-Wideband Radar Motion Sensor,” to McEwan produces a very narrowsensing region that is related to the transmitted impulse width. Atwo-pulse Doppler radar motion sensor, as described in U.S. Pat. No.5,682,164, “Pulse Homodyne Field Disturbance Sensor,” to McEwan,transmits a first pulse and after a delay generates a second pulse thatmixes with echoes from the first pulse. Thus a range gated sensing bandis formed with defined minimum and maximum ranges. UWB radar motionsensors have the disadvantage of not having global RF regulatoryacceptance as an intentional radiator. They also have difficulty sensingobjects at medium ranges and in some embodiments can be prone to RFinterference.

A modulated pulse Doppler sensor is described in U.S. Pat. No. 6,426,716to McEwan. The range gated microwave motion sensor includes adjustableminimum and maximum detection ranges. The apparatus includes an RFoscillator with associated pulse generating and delay elements toproduce the transmit and mixer pulses, a single transmit (TX)/receive(RX) antenna or a pair of separate TX and RX antennas, and an RFreceiver, including a detector/mixer with associated filtering,amplifying and demodulating elements to produce a range gated Dopplersignal from the mixer and echo pulses.

In U.S. Pat. No. 7,952,515, McEwan discloses a particular holographicradar. It adds a range gate to holographic radar to limit response to aspecific downrange region. McEwan states that cleaner, more clutter-freeradar holograms of an imaged surface can be obtained, particularly whenpenetrating materials to image interior image planes, or slices. Therange-gating enables stacked hologram technology, where multiple imagedsurfaces can be stacked in the downrange direction.

In U.S. Patent Application Publ. no. 2010/0214158, McEwan discloses anRF magnitude sampler for holographic radar. McEwan describes that the RFmagnitude sampler can finely resolve interferometric patterns producedby narrowband holographic pulse radar.

In U.S. Patent Application Publication No. 2014/0024917, McMahon et al,describe a sensor for physiology sensing that may be configured togenerate oscillation signals for emitting radio frequency pulses forrange gated sensing. The sensor may include a radio frequencytransmitter configured to emit the pulses and a receiver configured toreceive reflected ones of the emitted radio frequency pulses. Thereceived pulses may be processed to detect physiology characteristicssuch as motion, sleep, respiration and/or heartbeat.

There may be a need to improve sensors and/or their signal processingfor radio frequency sensing such as in the case of physiologicalcharacteristic detection when multiple sensors are in a common location.Sensor proximity can have undesirable interference. For example, thiscan deteriorate the signal to noise ratio.

SUMMARY OF THE TECHNOLOGY

One aspect of some embodiments of the present technology relates to asensor for detecting physiology characteristics with radio frequencysignals.

Another aspect of some embodiments of the technology relates to such asensor with a circuit configured to generate pulsed radio frequency (RF)signal that is transmitted towards a subject, e.g., a human. A receiverdetects signal reflected from the subject, which signal is amplified andmixed with a portion of the original signal. The output of this mixermay then be filtered. The resulting signal may contain information aboutthe movement, respiration and cardiac activity of the person, forexample, and may be referred to as the raw motion sensor signal. Thephase difference between the transmitted signal and the reflected signalmay be measured, either at the receiver or by an independent processor,in order to estimate any one of the general body movement, respirationand cardiac activity of the person.

In some versions, the RF motion sensors may be configured to reduceinterference from other RF motions sensors.

In some versions, the sensors may be configured to synchronize amongst agroup of local sensors to avoid overlap in RF pulses in time.

In some versions, the sensors may be configured to synchronize amongst agroup of local sensors to avoid overlap in RF pulses in frequency.

In some versions, the signal pulsing from each sensor may be adapted toreduce probability of interference by various means described herein,such as for example, by pulse width reduction, timing dithering and/orfrequency dithering.

In some versions, multiple (e.g., two) sensors may be configured, suchas with a common housing structure, to face in different or suitabledirections to avoid interference (e.g., placed midway along the bed atthe headboard or at feet).

In some versions, multiple sensors may allow for optimum placement tomitigate the noise. These versions could depend on the sensor antennapolarisation or antenna beam pattern to provide the necessary RFinterference attenuation.

Some versions of the present technology may include a radio frequencymotion sensor configured for operation in a multi-sensor configuration.The radio frequency motion sensor may include a radio frequencytransmitter. The transmitter may be configured to emit sensing signalssuch as pulsed radio frequency signals. The radio frequency motionsensor may include a receiver configured to receive reflected ones ofthe emitted radio frequency signals to detect motion of a reflectingsurface. The transmitter may be configured for synchronized transmissionof the pulsed radio frequency signals with another radio frequencymotion sensor in the vicinity of the radio frequency motion sensor tomitigate interference between emitted pulses from the radio frequencymotion sensors.

In some versions, the transmitter may be synchronized in time tointerleave emitted pulsed radio frequency signals with emitted pulsedradio frequency signals of another radio frequency motion sensor.Synchronization between the radio frequency motion sensors may involvetransmission of a clock signal. The synchronization between the radiofrequency motion sensors may involve transmission of a dithersynchronous signal. Optionally, the radio frequency motion sensordetects or may detect timing from an emitted pulsed radio frequencysignal. In some versions, the radio frequency motion sensor may detect asynchronization signal independent of the emitted pulsed radio frequencysignal. The radio frequency motion sensor may include an infra-redsignal transmitter adapted for timing of the emitted pulsed radiofrequency signals. The radio frequency motion sensor may include aninterface for wired connection with another radio frequency motionsensor. The wired connection may be configured for timing of the emittedpulsed radio frequency signals. The transmitter may be synchronized witha transmitter of another sensor with respect to frequency to reduceinterference.

Optionally, the transmitter may include a variable oscillator configuredfor frequency adjustment in response to detected interference noise. Thetransmitter may be further configured for frequency dithering. Thetransmitter may be further configured for time dithering. Thetransmitter may be configured to dither the frequency of the pulsedradio frequency signals.

Some versions of the present technology may include a radio frequencymotion sensor. The radio frequency motion sensor may include a radiofrequency transmitter configured to emit radio frequency sensing signalssuch as pulsed radio frequency signals; and a receiver configured toreceive reflected ones of the emitted radio frequency signals to detectmotion of a reflecting surface. The transmitter may be configured with adither timing different from a dither timing of another radio frequencymotion sensor in the vicinity of the radio frequency motion sensor tomitigate interference between emitted pulses from the radio frequencymotion sensors. The dither timing of the transmitter may be pseudorandom. The transmitter may be configured with frequency dithering.

Some versions of the present technology may include a radio frequencymotion sensing apparatus. The apparatus may include two or more radiofrequency sensors. Each sensor may include a radio frequency transmitterconfigured to emit sensing signals such as pulsed radio frequencysignals and a receiver configured to receive reflected ones of theemitted radio frequency signals to detect motion. The apparatus mayinclude comprises a housing to maintain the sensors in a configurationto emit the radio frequency signals in different directions to mitigateinterference between emitted pulses from the radio frequency motionsensors. The sensors may be so positioned to direct the emitted pulsesat a relative angle of about 90 degrees to 270 degrees. The sensors maybe positioned to direct the emitted pulses at a relative angle of about180 degrees or greater.

Some versions of the present technology may include a system fortransmitting radio frequencies such as for sensing. The system mayinclude a master radio frequency motion sensor and a slave radiofrequency motion sensor. The master radio frequency motion sensor may beconfigured to transmit a first radio frequency (RF) signal. The slaveradio frequency motion sensor may be configured to transmit a second RFsignal. The system may be arranged or configured to minimise theinterference between the RF signals of both sensors.

In some versions, the slave radio frequency motion sensor may beconfigured to transmit a second RF signal that creates minimalinterference with the first RF frequency signal. The master radiofrequency motion sensor and slave radio frequency motion sensor may beadapted within a single or common housing. The master radio frequencymotion sensor and slave radio frequency motion sensor may be positionedwithin the single or common housing at an angle of 90 degrees,approximately. The RF transmitter may be configured to transmit at leastone synchronization RE pulse signal. The slave radio frequency motionsensor may be further configured to receive the synchronization RF pulsesignal. The slave radio frequency sensor may be further configured todetect the received synchronization RF pulse signal at an intermediatefrequency. The master radio frequency sensor may be further configuredto transmit the at least one RF pulse signal on a separate industrial,scientific and/or medical transmission band (ISM). The master radiofrequency sensor may further include an infra-red (IR) transmitter suchas one configured to transmit an IR synchronization signal. The slaveradio frequency sensor may include an infra-red (IR) receiver such asone configured to receive the transmitted IR synchronization signal.

Optionally, the master radio frequency sensor and the slave radiofrequency sensor may further include a master-slave oscillator circuit.The master-slave oscillator circuit may further include a multi-wirecable interconnection such as one configured to transmit timing anddithering synchronization information from the master radio frequencysensor to the slave radio frequency sensor. At least one of the masterradio frequency motion sensor and the slave radio frequency motionsensor may include at least one resonator oscillator circuit. At leastone resonator oscillator circuit may include a quartz crystal.

In some versions, the slave radio frequency motion sensor may includethe at least one resonator oscillator circuit as well as a voltagecontrolled RF oscillator. The voltage controlled RF oscillator may beconfigured to synchronize its RF signal frequency to the master radiofrequency motion sensor. The voltage controlled RF oscillator may beconfigured to synchronize the RF frequency to the master radio frequencysensor by detecting a high voltage which result in a high level ofinterfering noise, detecting a low voltage which result in a high levelof interfering noise and moving the voltage controlled RF oscillator toa central control voltage position between the high and low voltage.Optionally, at least one of the first RF signal and second RF signal mayhave an RF pulse width of about 0.5 μs.

The master radio frequency sensor may be configured to provide a firstdithering time to the first RF signal. The slave radio frequency sensormay be configured to provide a different dithering time to the second RFsignal. The master radio frequency sensor may include a first binaryripple counter and exclusive OR gate. Similarly, the slave radiofrequency sensor includes a second binary ripple counter and exclusiveOR gate. The first and second binary ripple counter and exclusive ORgates may be configured to create a pseudo random dithering time. Themaster radio frequency sensor may include a first dielectric resonantoscillator that may be modulated by a first voltage. The slave radiofrequency sensor may include a second dielectric resonant oscillatorthat may be modulated by a second voltage. Optionally, the first andsecond RF signals may be at different frequencies.

Some versions of the present technology may include a system fortransmitting radio frequencies, such for sensing. The system may includea first radio frequency motion sensor and a second radio frequencymotion sensor. The first radio frequency motion sensor may be configuredto transmit a first radio frequency (RF) signal. The second radiofrequency motion sensor may be configured to transmit a second RFsignal. The system may be adapted to minimise the interference betweenthe RF signals of both sensors.

In some versions, the first frequency motion sensor may be configured toreceive an indication of the frequency transmitted from the second radiofrequency motion sensor, and the second radio frequency motion sensormay be configured to receive an indication of the frequency transmittedfrom the first radio frequency motion sensor. The first frequency motionsensor may be configured to adjust the frequency of the first radiofrequency signal in response to the received indication of the frequencytransmitted from the second radio frequency motion sensor. Each of thefirst frequency motion sensor and the second frequency motion sensor maybe configured to access a lookup table which includes selectablefrequencies at which the sensors can operate. The first frequency motionsensor may be configured to select a frequency from a first lookuptable, and the second frequency motion sensor may be configured toselect a frequency from a second lookup table. The first lookup tablemay include odd frequencies and the second lookup table may include evenfrequencies. The first frequency motion sensor and the second radiofrequency motion sensor may be configured to adjust their respectivefrequencies using a network time protocol (NTP).

The first frequency motion sensor and the second radio frequency motionsensor may be configured to adjust their respective transmissionfrequencies in response to detecting interference. The first frequencymotion sensor and the second radio frequency motion sensor may beconfigured to adjust their respective transmission frequencies based onpredetermined temperature coefficients. The first frequency motionsensor and the second radio frequency motion sensor may be configured tocheck or adjust the frequency at which they transmit RF signals inresponse to input of geographical location. At least one of the firstfrequency motion sensor and the second radio frequency motion sensor maybe configured to operate in a low power mode upon detection of anabsence of motion. The first frequency motion sensor and the secondradio frequency motion sensor may be configured to send a continuousclock signal over a wired or wireless link.

In some versions, at least one of the first frequency motion sensor andthe second radio frequency motion sensor may be configured to: sendperiodic centre frequency values read from each respective sensor over anetwork; and/or adjust the frequency at which each sensor transmits tominimise interference between the first and second sensors. At least oneof the first frequency motion sensor and the second radio frequencymotion sensor may be configured to: dynamically detect its respectivecurrent centre frequency; and/or periodically adjust such frequency inorder that it matches an agreed lookup table centre frequency so theinterference between the two sensors is minimized, while remainingwithin a defined spectral mask. Optionally, the first frequency motionsensor and the second radio frequency motion sensor may be configured sothat: a frequency range may be dynamically scanned to detect minimum andmaximum interference; and/or a centre frequency of at least one of thesensors may be adjusted to a frequency associated with the minimum. Thesensors may communicate via a frequency of maximum interference. Atleast one of the first frequency motion sensor and the second radiofrequency motion sensor may be configured to: detect a temperaturechange; and/or initiate polling between the sensors, based on thedetected temperature change, for adjusting a centre frequency of atleast one of the sensors.

In some versions, system may be arranged to minimise interferencebetween the RF signals of both sensors by frequency dithering of one ormore oscillators of the sensors generating the RF signals. For example,a voltage level to at least one of the one or more oscillators may beramped to produce the frequency dithering. The system may be arranged tominimise interference between the RF signals of both sensors by timingdithering of pulses of the RF signals of both of the sensors. Forexample, a voltage level to a diode coupled with at least one of the oneor more oscillators may be ramped to implement the timing dithering ofat least one of the sensors. In some cases, the at least one of the oneor more oscillators may be a dielectric resonant oscillator.

Other aspects, features, and advantages of this technology will beapparent from the following detailed description when taken inconjunction with the accompanying drawings, which are a part of thisdisclosure and which illustrate, by way of example, principles of thetechnology. Yet further aspects of the technology will be apparent fromthe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Further example embodiments of the technology will now be described withreference to the accompanying drawings, in which:

FIG. 1 is an illustration of an example detection system suitable forimplementation with a radio frequency physiology sensor of the presenttechnology;

FIG. 2 is a conceptual diagram illustrating a an operation of someembodiments of the technology;

FIG. 3 is a diagram illustrating a conceptual structure and process flowfor obtaining sensor signals suitable for some embodiments of thetechnology;

FIG. 4 shows example components involved in a generation of range gatedradio frequency signals with switched oscillation in some embodiments ofa sensor circuit for the present technology;

FIGS. 5A and 5B are diagrams illustrating the creation and detection ofan RF pulse suitable for some embodiments of the technology;

FIG. 6 is an illustration of the resultant receiver RF signal suitablefor some embodiments of the technology;

FIG. 7 is an illustration of the transmitted signal (700), receivedsignal (702) and the resultant receiver RF signal (704); which includesbaseband noise, as described in the present technology. The constantvariations seen in the resultant receiver RF signal (704) may lead tobaseband interference;

FIGS. 8A and 8B are diagrams showing examples of signal paths travelledby RF signal as found in some embodiments of the present technology;

FIG. 9 is a diagram representation of sensor positions suitable for someembodiments of the present technology;

FIG. 10A is a signal representation of synchronous timing of the pulsegeneration.

FIG. 10B is a signal representation of “dithering” of the pulsegeneration;

FIG. 11A is a signal representation of asynchronous timing of the pulsegeneration and reading;

FIG. 11B is a signal representation of overlapping signals as describedin the present technology;

FIG. 12 is a diagram of an IR-Signal timing connection suitable for someembodiments of the present technology;

FIG. 13 is a three wire synchronous master slave test circuit as used insome embodiments of the technology; and

FIG. 14 is an example of housing suitable for some embodiments of thetechnology.

FIG. 15 shows a sample ratio between a sensor baseband range, anintermediate frequency and a filter range.

FIG. 16A is a signal graph with exemplar in-phase and quadraturebaseband signals in the time domain with no interference.

FIG. 16B is a signal graph with an intermittent interfering signal.

FIG. 16C is a signal graph with peak noise greater than 200 mVrms, wherethe timing of the peak noise level is unpredictable.

FIG. 17 shows a sample schematic of how RF modulation and demodulationtiming is established by a 4 MHz ceramic resonator oscillator andassociated binary ripple counter.

DETAILED DESCRIPTION 1. Overview

As illustrated in FIG. 1, some embodiments of the present technology mayimplement sensing or detection apparatus 100 and 102, useful fordetecting physiological characteristics of multiple users or patients.The sensors may be standalone sensors or may be coupled with otherapparatus, such as a respiratory treatment apparatus, so as to providean automated treatment response based on an analysis of thephysiological characteristics detected by the sensors of the apparatus.For example, a respiratory treatment apparatus with a controller and aflow generator may be configured with such a sensor or to communicatewith such a sensor and may be configured to adjust a pressure treatmentgenerated at a patient interface (e.g., mask) in response tophysiological characteristics detected by the sensor. Or such a sensormight be used to detect physiological characteristics of a patient whenthe flow generator is not in use by the patient to inform them of theadvantage of using the flow generator. An example respiratory treatmentapparatus is described in International Patent Application No.PCT/US2015/043204, filed on Jul. 31, 2015, the entire disclosure ofwhich is incorporated herein by reference.

A typical sensor of such an apparatus may employ a transmitter to emitradio frequency (RF) waves, such as radio frequency pulses for rangegated sensing. A receiver, which may optionally be included in acombined device with the transmitter, may be configured to receive andprocess waves reflected from the patient's body. Signal processing maybe employed, such as with a processor of the apparatus that activatesthe sensor, to derive physiological characteristics based on thereceived reflected signals. An example of the operation of such a sensorcan be found in U.S. Patent Application Publ. No. 2009/0203972, theentire disclosure of which is incorporated herein by reference.

A principal diagram of a sensor, or of a component of the sensor, isshown in FIG. 3. As illustrated in FIG. 3, the transmitter transmits aradio-frequency signal towards a subject, e.g., a human. Generally, thesource of the RF signal is a local oscillator (LO). The reflected signalis then received by the RF receiver, amplified and mixed with a portionof the original signal, and the output of this mixer may then befiltered. The resulting signal may contain information about themovement, respiration and cardiac activity of the person, for example,and is referred to as the raw motion sensor signal. The phase differencebetween the transmitted signal and the reflected signal may be measuredin order to estimate any one of the movement, respiration and cardiacactivity of the person.

The raw motion sensor signal can be processed to obtain signalcomponents reflecting bodily movement, respiration and cardiac activity.Bodily movement can be identified by using zero-crossing or energyenvelope detection algorithms (or more complex algorithms), and used toform a “motion on” or “motion off” indicator. For example, such movementdetection algorithms may be implemented in accordance with themethodologies disclosed in any of U.S. Patent Application Publ. No.2009/0203972, mentioned previously, International Patent ApplicationNo., PCT/US14/045814; U.S. Provisional Patent Application No.62/149,839, filed Apr. 20, 2015, and U.S. Provisional Patent ApplicationNo. 62/207,687, filed Aug. 20, 2015, the entire disclosures of which areeach incorporated herein by reference. The respiratory activity istypically in the range 0.1 to 0.8 Hz, and can be derived by filteringthe original signal with a bandpass filter with a passband in thatregion. The cardiac activity is reflected in signals at higherfrequencies, and this activity can be accessed by filtering with abandpass filter with a pass band of a range from 0.8 to 10 Hz (e.g., 70heart beats per minute is within this range at around 1.17 Hz).

Such a respiration and movement sensor may be a range gated RF motiondetector. The sensor may be configured to accept a DC power supply orbattery input and provide, for example, four analog motion channeloutputs with both in-phase and quadrature components of the respirationand movement signals of a person within the detection range. In the caseof a pulsed RF motion sensor, range gating can help to limit movementdetection to only a preferred zone or range. Thus, detections made withthe sensor may be within a defined distance from the sensor.

As illustrated in FIG. 4, a typical sensor 402 of the present technologymay employ one or more oscillators, such as an oscillator 404, such as adielectric resonant oscillator (DRO). The DRO may be a high Q DRO thatis a narrowband oscillator (e.g., a DRO operating at 10.525 GHz), suchas an oscillator incorporating a puck of dielectric material. The DROtypically generates a stable RF frequency characteristic and isrelatively immune to variation in temperature, humidity and componentparasitics. In some cases, the sensor may be a sensor described in U.S.Patent Application Publication No. 2014/0024917, the entire disclosureof which is incorporated herein by reference.

As illustrated in FIG. 5A, the pulsed radio frequency signal has twomain modulation parameters. These are the pulsed repetition interval(PRI), with time duration represented by T, and the pulse width (PW),with time duration represented by T. The term pulsed repetitionfrequency (PRF) is the inverse of the PRI. For example, a sensor maytransmit a 10.525 GHz RF signal which was pulse modulated at a frequencyof approximately 250 KHz to create an RF pulse signal with a pulserepetition interval designated τ of 4 μs and a pulse width timingdesignated τ of 2 μs. Accordingly, the RF signals in the example wouldbe 0.5 μs long and produced every 4 μs (i.e., a 12.5% duty cycle).

The sensor may be a homodyning transceiver capable of both transmittingand receiving RF signals. As such, the transceiver may measure themagnitude and phase of the received signal with respect to thetransmitted signal. The phase and/or magnitude of the received signalchanges with respect to the transmitted signal when the target moves orupon the distance the received signal travelled. As a result, thedemodulated magnitude detector receiver output signal is a measure ofthe movement of a target and/or the distance the signal travelled. Whilesuch a magnitude detector may be optionally implemented, in some cases,other circuit elements or detectors may be implemented in place of or toserve the function of the magnitude detector(s). For example, anydetector circuit configured to detect signal modulation, such as a peakdetector, envelope detector, or harmonic mixer circuit may be employed.

Both transmitted RF signals and received RF signals may be presented tothe input of a homodyning receiver switched magnitude detector (e.g., anRF magnitude detector). For example, as shown in FIG. 5B, a receivedsignal may be detected during a receive time interval period when thesensor is transmitting an RF pulse. In this regard, the magnitudedetector may detect RF pulses every time an RF pulse is transmitted. Insome embodiments, the magnitude detector may detect signals during a 5ns period during the first 12 ns of a RF pulse transmission (i.e., the 5ns could be anywhere within the first 12 ns, e.g. starting at the 7^(th)ns, ns etc.).

When only a single source of RF pulses is present, the transmitted andreceived RF signals may be represented with the following mathematicalformulas:

Transmitted RF signal: A Sin(ω1t+θ1); and

Received RF signal: B Sin(ω1t+θ2)

Where A and B are amplitudes, ω1 is the angular frequency, t is thetime, and θ1 and θ2 are respective phases. (Time travelled is implicitin the phase difference between θ1 [e.g., reference phase at oscillator]and θ2 [after bouncing off the subject]).

As the two signals are from the same source, they also have the samefrequency. Accordingly, when they are superimposed the resulting RFsignal has an amplitude that varies with phase and amplitude of thereflected signal. The transmitted RF signal and received RF signal maybe combined by using the following formulas where a and b areamplitudes, x is a time multiplied angular frequency (2ηft), and β and αare phases.

As shown in FIG. 6, a resulting signal 602 may be the result of atransmitted RF signal being modulated by a received RF signal. Theresulting signal 602 may have a periodic sinusoidal amplitude envelope600 and phase that varies only respective of distance and movement of atarget. Accordingly, the superimposed signal varies with the distance toa target or target movement.

Time Dithering

When operating two or more sensors, oscillator timing differences and/ordithering may promote noise interference reduction. For example, in somesensors, the timing of the pulse generation may be dithered with respectto the timing associated with the underlying pulse repetition frequencyby inclusion of a dithering circuit (not shown) such as one coupled withor included with a pulse generator 408. FIG. 10b shows a signalrepresentation of “dithering” of the pulse generation (in which theonset time of the pulse varies with respect to the overall pulsegeneration timing). With such dithering, the overall pulse repetitionfrequency can be varied, so that the pulse onset time is linearlydelayed or advanced with respect to the nominal overall pulse center(i.e., a second pulse train is at a slower pulse repetition frequencythan a first pulse train). This has the net effect of changing theposition of the pulse onset time, compared to its nominal onset time ifthe PRF remained fixed. This may be achieved with a synchronous rampdithering circuit. An example synchronous ramp dithering circuit may beimplemented with a voltage controlled delay element based on anunderlying RC (resistor-capacitor) time constant. The ramp controlvoltage results in a varying varactor capacitance which in turn resultsin a varying resonator frequency. In this way the frequency of the pulsegeneration circuit oscillator and associated PRF is varied on the orderof about 1% in a synchronous and linear manner every 1 ms approximately.In some examples, the linear ramp function may be at 1 kHz, whichproduces an associated dither on the PRI and PW timing. Dithering may beutilised to remove synchronous RF demodulation noise artefacts. Rampdithering may be utilised because it is less complex to implement,however it can produce tone artefacts if not synchronous with the RFmodulation and demodulation timing. Synchronous ramp dithering preventsthese unwanted tones from being generated. However, the use of a timingdithering circuit complicates the unit to unit PRI timing difference andhence complicates pulse timing synchronization.

In some sensors, RF modulation and demodulation timing is established bya 4 MHz ceramic resonator oscillator and associated binary ripplecounter (see example of FIG. 17). To achieve low demodulation noise, theoscillator timing may be subsequently “synchronously dithered” with alinear ramp function (e.g., at 1 kHz) which produces an associateddither on the PRI and PW timing. This use of a timing dithering circuitcomplicates the unit to unit PRI timing difference. This timingdifference is further compounded by the use of a ceramic resonator whichhas a lower frequency tolerance and higher drift compared to that of aquartz crystal. In summary, although synchronous dithering can mitigateRF interference signal noise it creates issues for a second method of RFinterference signal noise reduction, namely pulse timingsynchronization, due to dithering and/or the timing difference. Forexample, as shown in FIG. 10A the read signals of the 1^(st) sensor mayoverlap with the pulse of the 2^(nd) sensor and vice-versa.

For two sensors to coexist without producing RF interference the firstsensor should transmit its RF pulse in the quiet period of the secondsensor and vice versa. For example, as shown in FIG. 11A, the readsignals (white lines/indicated as “RL” on the Figure) of the firstsensor occur only during the time periods during which the second sensoris not transmitting a RF signal. Similarly, the second sensor only readssignals when the first sensor is not transmitting. However, in practicethe asynchronous nature of the sensor operations (dithering, frequencydifference and frequency drift) results in periodic overlap of the RFpulse of the first sensor with the receive timing of the second sensor,as shown in FIG. 11B. In this regard, due to the nature of the sensors,the read signals of the first sensor may occur during the transmissionof an RF pulse by the second sensor and vice-versa.

2. Sources of Noise

Sensors, such as the sensors of illustrated detection apparatus 100 and102 which are positioned within close proximity of each other, maysuffer from radio frequency (RF) coexistence issues. As illustrated inFIG. 2, two sensors 300 and 302 may be placed so that their respectiveRF pulses are projected in the direction of the opposing sensor. In thisregard, sensor 300 may transmit RF pulse 312 in the direction of sensor302, and sensor 302 may transmit RF pulse 310 in the direction of sensor300. As a result, the sensor 300 may receive the reflection of its RFpulse 312, the direct RF pulse 310 of the opposing sensor 302, as wellas the opposing sensor's double-reflection RF pulses (not shown).Accordingly, the RF pulses received by a sensor may include more thanjust the desirable RF pulse reflections created by the RF signal thatthe sensor originally transmitted, resulting in baseband interferencewhen the received RF pulses are demodulated. (Generally, in some cases,a baseband signal may be a signal that has a very narrow frequencyrange, i.e. a spectral magnitude that is nonzero only for frequencies inthe vicinity of the origin (termed f=0) and negligible)).

While only RF pulses of the sensors are shown in FIG. 2, RF waves fromother apparatus may also be received by the sensors. Such RF waves maycome from apparatus located both near and far from the sensors. Due tothe nature of RF waves, they may possess the ability to travel throughbarriers such as walls and other obstacles and geographical topography.Accordingly, embodiments of the present technology may be directed tosignificantly diminishing the sensors' susceptibility to RF coexistenceissues.

When received RF signals come from an apparatus or source other than thetransmitting sensor, noise may be introduced into the received RFsignals. The transmitted, received and resultant RF signals may berepresented with the following mathematical formulas:

RF signal transmitted by the first source:

A Sin(ω₁ t+θ1); and

RF signal received at the second source:

A Sin(ω₂ t+θ2)

Resultant Combined RF Signal:

${{A\; \cos \; 2\pi \; f_{1}t} + {A\mspace{11mu} \cos \; 2\pi \; f_{2}t}} = {2A\; \cos \; 2\pi \frac{f_{1} - f_{2}}{2}t\mspace{11mu} \cos \; 2\pi \frac{f_{1} + f_{2}}{2}t}$

Where A and B are amplitudes, ω₁t and ω₂t are respective time dependentangular frequencies, and θ1 and θ2 are respective phases. Combining thetransmitted signal from the first source and received RF signal from thesecond source may result in an RF signal with a periodic sinusoidalamplitude envelope and phase that constantly varies in time irrespectiveof any movement of a target. In the example of FIG. 7, transmittedsignal 700 from a first source may be combined with a signal 702received from a second source, producing resulting signal 704. As can beseen, the resulting signal 704 has a periodic sinusoidal amplitudeenvelope and phase that constantly varies in time irrespective of anymovement of a target. (As the phase is constantly changed with time,this is represented as a circle in FIG. 7 [left hand side]). Suchconstant variations to the resulting signal may be introduced when thereceived signal 702 is combined with the transmitted signal 700 at amultiple of the intermediate frequency of the transmitted frequency.Such variations may lead to baseband interference.

The amount of interference generated by an RF signal transmitted from anapparatus or source other than the receiving sensor may be dependent onthe received signal strength of the unwanted interfering RF signal. Inthis regard, the unwanted interfering RF signal's strength may bedependent upon the path the interfering RF signal travels beforearriving at the receiving sensor. For example, as shown in FIG. 8A, aninterfering signal 806 may be reflected off of an object 804 andreceived by the receiving sensor 800. Accordingly, the power of theinterfering RF signal 806 is reduced when it arrives at the receivingsensor 800, compared to the case when the signal arrives directly at thereceiving sensor 800. The formula for the power of the interferingsignal after being reflected is given by:

$P_{r} = \frac{P_{t}G_{t}A_{r}\delta \; F^{4}}{\left( {4\pi} \right)^{2}R_{r}^{4}}$

Wherein:

P_(r)=power of the interfering signal which has been reflected;

P_(t)=transmitter power;

G_(t)=gain of the transmitting antenna;

A_(r)=effective aperture (area) of the receiving antenna (most of thetime noted as Gr);

δ=radar cross section, or scattering coefficient, of the target;

R_(r)=distance from the transmitter to the target (for a reflectedsignal) and

F=pattern propagation factor (Normally close to 1)

In contrast, as shown in FIG. 8B, an interfering signal 808 may begenerated by a second active source 802 and received directly by sensor800, without incurring any reflections. As no reflection of theinterfering signal 808 occurs, the power of the interfering signal 808is only reduced based on distance travelled. Accordingly, the power ofthe interfering RF signal is reduced based on distance. The formula forthe power of the interfering signal 808 which has not been reflected butdirectly arrives at the receiver is given by:

$P_{d} = \frac{P_{t}G_{t}A_{r}\delta \; F^{4}}{\left( {4\pi} \right)^{2}R_{d}^{2}}$

Wherein:

P_(d)=power of the interfering signal which has not been reflected;

P_(t)=transmitter power;

G_(t)=gain of the transmitting antenna;

A_(r)=effective aperture (area) of the receiving antenna (most of thetime noted as Gr);

δ=radar cross section, or scattering coefficient, of the target;

R_(d)=distance from the transmitter to the receiver. (for a directtransmit to receive); and

F=pattern propagation factor (Normally close to 1)

As a result, when two sensors are placed in a room, the interferingsignal level from the second unit can be higher than the signaltransmitted by the first sensor and reflected back to the first sensorbecause of the shorter effective path length and the absence ofattenuation due to scattering.

When an interfering RF signal is received at a sensor, the interferingRF signal will cause baseband noise under certain conditions: (1) theinterfering RF frequency is in-band (i.e. close to 10.525 GHz, 10.587GHz, 9.3 GHz, 61 GHz, 24 GHz, 10.45 GHz), (2) the interfering RF signalis received during the receive time interval of the sensor, (3) thefrequency of the RF signal transmitted by the sensor and the frequencyof interfering RF signal have a difference frequency that is a multipleof the pulse repetition frequency of the transmitted frequency signal,and (4) the RF interfering signal has a sufficient amplitude to producean interfering noise signal.

These four conditions may be restated as follows, where RF1 representsthe main sensor's RF centre frequency, RF2 represents the interferingsources RF centre frequency, IF1 represents the intermediate frequency(Generally, in some cases, such as in communications and electronicengineering, an intermediate frequency (IF) may be considered afrequency to which a carrier frequency is shifted as an intermediatestep in transmission or reception) of RF1, and IF2 represents theintermediate frequency of RF2:

(1) Interference may occur when RF2 is within the demodulation frequencyrange of RF1, typically by +/−25 MHz;

(2) Interference may occur when the pulse repetition frequency of RF2(PRF2) is a multiple of the RF1 frequency. More specifically, ifRF1=RF2+/−n(PRF2), where n is any integer;

(3) Because the receiver is a synchronous phase detector interferencemay occur when the information on demodulated RF2 includes the frequencyof IF1 or any of its odd harmonics. Stated another way, RF2 (i.e., asignal which has been modulated by AM/FM modulation, or any othermodulation scheme) contains information on the IF1 or its odd harmonics;

(4) Interference may occur when RF1 and RF2 are combined and thensubsequently demodulated, where RF2 is of sufficient signal level toproduce a baseband noise component.

To curtail such baseband noise interference, the present technologycontemplates implementation of several solutions. First, the sensors maybe synchronized in time to avoid any overlap in RF pulses in time.Second, the sensors may be synchronized to avoid overlap in RF pulses infrequency (i.e., RF1=RF2+/−(n+0.5)(PRF2)). Third, the sensors may beconfigured to pulse in such a way that the probability of interferenceis negligible. Fourth, two or more sensors may be placed in one housingfacing in different directions (e.g., placed midway along the bed at theheadboard or at feet). Examples of each of the implementations aredetailed herein.

For the case of a range gated RF sensor using a DRO as a referenceoscillator, a second or subsequent sensor can have such a stable emittedfrequency and behaviour, that it becomes a nearly optimal interferer tosimilar sensors that are nearby (i.e., when considering a multiplenon-contact range gated sensor system).

In order to mitigate this interference for effective low noise operationwhere more than one sensor is in proximity the following implementationsmay be made:

-   -   (i) timing synchronization can be implemented between the        sensors via a wire or wirelessly (where precise timing signals        are used between cooperating sensors), or    -   (ii) each sensor can be configured to independently behave in a        manner that does not cause this nearly perfect interference        (without requiring cooperation).

For the latter case (i.e., with no inter-sensor cooperation), ditheringin both time and/or frequency may be used. Dithering of timing may beused to spread the noise, while frequency dithering may be used toprevent interference. For example, as discussed in more detail herein,in some embodiments ramping of the voltage on a diode coupled to atiming oscillator can change diode capacitance. This leads to a changein the frequency of oscillation of the timing oscillator, resulting intiming dithering, such as by dithering timing pulsed involved in thegenerated pulsed RF signals. Additionally, by ramping the supply voltageof the DRO (Dielectric Resonant Oscillator), the frequency is changedresulting in frequency dithering (e.g., by ramping voltage 2.5-3.0-2.5V)of the RF signals.

3. Timing Synchronization

Time synchronizing of the RF pulses may be implemented by generating asynchronizing pulse from the first sensor (master) to the second sensor(slave). As such, the second sensor would transmit its RF pulse in thequiet period of the first sensor. This solution may have the same noiselevel as shown in the “baseline noise” setup of FIG. 9. Instead of by amaster sensor, the synchronization of all sensors could be driven by anindependent controller in a very similar way to that used by a mastersensor to drive one or more slave sensors. Or indeed the sensors couldact as peers, e.g., control and communication is distributed amongdevices in the field, whereby each device communicates directly with thedevices around it without having to go through/via a master device.

In order to implement timing synchronization between sensors thefollowing factors may be considered. First, the timing of the sensorsmay include synchronous dithering such as at a 1 ms interval, or more orless, so synchronization may not be easily achieved. Second, the timingof the sensors may be controlled by a ceramic resonator, with only about1% frequency accuracy. Third, the slave unit should be enabled to detectloss of synchronization and maintain the sensor timing. Fourth, both aclock and dither synchronous signal can be transmitted from the masterto slave sensor such as to help address issues of the use of ditheringand the asynchronous nature of the operations. Fifth, synchronizationshould be achieved with sub-micro second timing accuracy to maintain therequired RF pulse interleave locking. Sixth, the master and slavesensors should know they are required to transmit or receive thesynchronization signal. (i.e., the sensors should automaticallysynchronize when required or be set at installation to synchronize)

3.1 RF Pulse Signal

Arising from these considerations, particularly in view of the ditheringand asynchronous nature of the timing, some versions may includegeneration of a timing synchronization that includes transmission ofboth a clock and a dither synchronous signal, and which may be with submicro second timing accuracy. There are a number of ways of achievingthis, including detecting the RF pulse signal from the master unit. Inthis regard, when the pulse signal from the master unit is received bythe slave units, the timing of the slave units are adjusted to assurethe slave units do not transmit an RF signal at the timing associatedwith the pulse signal of the master unit. However, a change of timingarchitecture may be required as the RF pulse signal may not be at theclock frequency of the oscillator. Additionally, the implementation of aphase-locked loop (PLL) may be required but may be complicated by thedithering. If timing dithering is not employed then the synchronizationrequirements above are reduced to that of PRF pulse timingsynchronization, which is a lesser requirement. Pulse timing ditheringmight not be employed and instead enhanced interference noise reductionmay be achieved by RF frequency dithering in some cases.

3.2 RF Pulse Signal Detection at Intermediate Stage

Another method for transmitting both the clock and dither synchronoussignal with sub micro second timing accuracy is by detecting the RFpulse signal of a master sensor at the IF (intermediate frequency) stageby the slave sensor. Because of circuit complexity to receive, amplifyand condition the receive signal and in addition to phase lock it to thelocal 4 MHz oscillator, this solution is not easily implemented, howeverit is feasible, especially if digital sampling is employed.

3.3 Separate RF Signal

In another method, a separate RF synchronization signal may be sent. Forexample, a separate industrial, scientific, and medical band (ISM) RFsignal may be generated to provide the synchronization signals from themaster unit to slave units. In this regard, through a wireless means theISM RF signal could potentially be piggy-backed on an existing RFcommunications channel.

3.4 Other Wireless Signal

In an alternate method, timing synchronization can be implementedthrough other wireless communications methods, including RF signals suchas Bluetooth, Wi-Fi, ZigBee or other proprietary wireless means.

3.5 Infra-Red Signal

In an alternate method, timing synchronization can be implemented byphotonic means such as through light pulses and specifically through aninfra-red signal. As shown in FIG. 12, a master sensor 1201 could sendan infra-red signal 1204 to slave sensor 1202. In this regard, themaster sensor 1201 may include an infra-red transmitter/receiver and theslave sensor 1202 may include an infra-red transmitter/receiver.Accordingly, the master sensor 1201 may transmit timing signals from theinfra-red transmitter to the infra-red receiver of the slave sensor1202. However, complications achieving the required coverage and speedrequired for timing accuracy may be presented. For example, depending onthe distance between the sensors, the infra-red signal may be delayed,thereby not providing proper synchronization. Further, interferenceissues such as a high speed IR signal “jamming” output from otherdevices (e.g., a television remote control) may be encountered. Othermethods, such as fibre optic connection or transmission via visiblelight communication (e.g., pulsing LEDs or fluorescent lamps) in therange between 400 and 800 THz (780-375 nm) could also be used.

3.6 Wire Cable Coupling

Another method of timing synchronization can be implemented through awired connection. For example, a multi-wire cable (e.g., a three wirecable or a two wire cable, etc.) may be used to connect a master sensorto a slave sensor. Such a three wire cable synchronous master-slaveoscillator circuit is shown FIG. 13. The three wire cable may connectthe master sensor to a slave sensor, thereby enabling the master sensorto transmit timing and dithering synchronization information from themaster sensor to the slave sensor. On the left side of FIG. 13 is themaster sensor circuit 1301, and on the right side of the figure is theslave sensor circuit 1302. The master sensor circuit may include a ResetU1 pin 11 connected to ground via 1k resistor to enable reset control(not shown). Additionally, the master sensor circuit 1301 may include a4 MHz oscillator input U1 CLK pin 10 buffered by a gate driver/buffer(and supplied as a clock output to the slave. Further, the master sensorcircuit may include a 1 kHz dither output U1 Q12 pin 1 buffered by gatedriver/buffer which is supplied as a reset output to slave. Finally, themaster circuit may be connected to ground (0V) and supplied as output tothe slave sensor.

The slave sensor circuit may include Reset U1 pin 11 connected to groundvia 1k resistor to enable reset control, as well as a 1 kHz ditheroutput, received from the master circuit, and presented to the slavecircuit Reset U1 pin 11 via 2.2 Nf series capacitor. The slave sensorcircuit may further include a 4 MHz oscillator output gate driver/bufferreceived from the master circuit to drive transistor Q1 collector via a1 kHz resistor. Finally, the slave circuit may include a circuit ground(0V) supplied as input from the master circuit.

In more general terms, the master clock output is transmitted through afirst buffer (on the master circuit) to a wire which is received by asecond buffer on the slave circuit. The output from the second buffer ispresented to the slave clock input. Similarly the reset output istransmitted through a buffer to a wire which is received by a buffer onthe slave circuit. The output from the second buffer is presented to thereset pin through a differentiator circuit/high pass filter. Only theleading edge of the reset pulse is passed through to the reset pin. Theslave circuit may be connected to ground.

The master and slave sensors may be synchronized by a three wire cableby sending, from the master sensor, a pulse width of around 0.5 us forexample. Such a pulse width enables out of phase synchronization of theRF pulses.

As already stated, if timing dithering is not employed then thesynchronization requirements above are reduced to that of PRF′ pulsetiming synchronization which is a lesser requirement. In this case thethree wiring timing circuit described reduces to that of a two wiretiming circuit. A two wire circuit can be implemented by transmittingthe master reset output and letting the clocks run. This removes themaster clock requirement.

A wired connection can achieve synchronization requirements and can alsooptionally provide other functions. For example, the wire cable could beimplemented to power a second (or subsequent) unit(s). As such, the wiremay allow for more remote sensor placements while not necessarilyintroducing more wires and cables. In addition the two wires couldprovide timing synchronization and power to a second unit by modulatingthe signals. The wire could also reduce the need for other wirelesschipsets; e.g., a set of sensors may form a pair, with only one of themhaving a Wi-Fi or Bluetooth interface and power adaptor or space forbatteries, and the second simply connected via cable and not having aneed of a separate Wi-Fi etc. radio capability as relevantcontrol/sensor data are also modulated onto the wire. A more complexwired connection based on Ethernet could also be used.

Both the three wire and two wire synchronization circuits describedabove could be implemented on the circuitry of the sensor or could belocated in the connecting wires. The advantage of the latter would bethat synchronization circuitry and associated cost would not be includedin every unit.

3.7 Quartz Crystal

Either in addition to the above timing synchronization solutions, or asa stand-alone solution, the oscillator may be implemented with a quartzcrystal. Accordingly, less frequent synchronization signals will benecessary as the quartz crystal has a high frequency tolerance and lowfrequency drift rate. Additionally, only a single synchronization signalis necessary (e.g., clock), as a quartz crystal may be implementedwithout dithering.

4. Frequency Synchronization

Another implementation to reduce RF interference between multiplesensors is to synchronize the RF frequencies of the sensors. In thisregard the sensors can coexist without producing RF interference. Forexample, if two sensors transmit at RF frequencies, f1 and f2,respectively at time t, the receive signal due to f1 and f2 is:

${{A\; \cos \; 2\pi \; f_{1}t} + {A\mspace{11mu} \cos \; 2\pi \; f_{2}t}} = {2A\; \cos \; 2\pi \frac{f_{1} - f_{2}}{2}t\mspace{11mu} \cos \; 2\pi \frac{f_{1} + f_{2}}{2}t}$

Maximum interference between f1 and f2 occurs when f1−f2=n*PRF±IF,wherein IF is an intermediate frequency, and n is an integer. Minimuminterference occurs when f1−f2=(n+0.5)*PRF+IF.

4.1 Differing Frequencies

To minimize interference, different sensors may be configured fordifferent frequencies. In this regard, sensors may be dynamically set todifferent frequencies. For example, the sensors may implement a DROwhose frequency is a function of voltage. For example, a variation of 1VDC may result in an RF frequency change of 1.5 MHz.

The voltage controlled RF oscillator of the first sensor may synchronizeto the RF frequency to the second unit. In this regard, a controlcircuit within the first sensor can adjust the DRO voltage to a minimumnoise voltage by detecting the DRO voltages which result in a high levelof interfering noise and by moving to a central control voltage position(i.e. an area of low noise) between these two “high noise level”voltages (e.g., where there is a pattern of constructive, destructive,constructive, destructive etc. interference gives rise to multipleinterference maxima. RF frequency synchronization between two sensorshas been demonstrated to produce the same noise level as if only asingle sensor was in use.

4.2 Automatic Detection of Interference and Communication BetweenSensors Via a Wired or Wireless Network, or Via Coded Interfering Pulses

Another way of minimizing interference is by having each of a pluralityof sensors detect their own respective centre frequency. Each sensor maythen transmit their respective frequency value to the other sensors overa wired or wireless connection. The sensors may then adjust theirrespective centre frequencies to achieve an optimal spacing in order tomaximally reduce interference between each other. In this manner, themore than one sensors can cooperate to reduce or avoid interference.Such a configuration may avoid the need to transmit a clock signal,clock edge, and/or a reset. Also this approach may be tolerant of delaysand other potential issues that may arise in a communications channel,thereby allowing the sensors to operate over a link with poor quality ofservice (QoS). However, such an approach is not limited to poor QoSnetworks, and could be implemented on QoS links with good or highquality. Further, transmitting respective centre frequencies couldpotentially avoid the use of buffer circuits (unless required),dedicated cables, and/or synchronize radio or infra-red links. Incontrast, transmitting a clock signal, clock edge, and/or resetconstantly between sensors may require a defined QoS including latency,bandwidth, and other parameters. A network such as the Internet or anad-hoc peer to peer Wi-Fi link such as Wi-Fi Direct using Wi-FiProtected Setup (WPS) are examples of such a link (e.g., these areexamples of links suitable for centre frequencies transmission or for aclock signal transmission).

Detection of a centre frequency may require a few additional circuitcomponents amount of circuitry (e.g., tapping a signal from the mixer),and may be enabled by a digital sensor. In this regard, a first digitalsensor may send a notification of its most current or recent centrefrequency reading, to a second digital sensor, and the second digitalsensor may send its most current or recent centre frequency reading tothe first sensor. For example, the first digital sensor may send acentre frequency of 10.252791 GHz and the second digital sensor may senda centre frequency of 10.525836 GHz. The first and second digitalsensors may then adjust their respective centre frequencies to achievean optimal spacing, of for example, 125 kHz, in order to maximallyreduce interference between each other. The optimal adjustment amountmay be based on the IF and PRF configuration of the respective sensors.Although a digital sensor is described, transmittal of a frequency valuemay also be enabled by an analogue baseband sensor configured to shareinformation with a processor in an attached device.

Transmittal of the centre frequencies may occur over a Wi-Fi, Ethernet,Bluetooth, or any other type of connection. Transmission may involve anauthentication handshake and then periodic transmission of centrefrequency values. Optionally, transmission of updated values may occurwhen the values deviate by a defined threshold from a past value. Insome embodiments the transmitted data may be encoded in packets over theWi-Fi link.

4.3 Frequency Lookup Table

Another technique to establish frequency synchronization is to uselookup tables of frequencies in each sensor. In this regard, sensors mayeach store copies of lookup tables (or functions or formula todynamically calculate such frequencies). For example, a table or tablesmay include a set of odd frequencies and a set of even frequencies. Theodd and even frequencies may be chosen to sit at nulls in mutualinterference. The sensors may then be programmed to select a frequencyto operate at from the odd and even tables. As such, the tables may spana region within an allowable spectral mask of a filter associated with asensor, wherein the region is within the controllable centre frequencyrange of the sensor. For example, the frequencies may be selected from:

(0.5+n)*PRF;

Where n is an integer and PRF is a pulse rate frequency. In the casewhere sensors may be programmed to calculate frequencies using amathematical formula as needed, such a configuration may permit areduction in sensor memory.

In certain embodiments, a first sensor might check if it is operating ator near a frequency in either the even table or the odd table, and makeminor adjustments to match one of these close (or closest) frequencieson either table. For example, the first sensor might adjust itsfrequency to the nearest frequency in the even table. A second sensormay then adjust its frequency to the nearest frequency in the odd table,thereby achieving minimal interference.

Communication between a defined pair (or plurality) of sensors may onlyhave to happen once at setup. As such, a defined pair configuration mayhelp remove the need for an ongoing wired or wireless transmissionbetween the sensors. Accordingly, complexities introduced by continuallyupdating the frequencies during ongoing operation may be minimized orremoved.

The one-off pairing process for a defined pair (or plurality of sensors)could be performed via wired or wireless means. For example, near fieldcommunications (NFC) and/or an accelerometer could be used to enable“tap to pair,” whereby close proximity and/or a control signal is usedto enable the communication of the table information between sensors.

Alternatively, the pairing process could be repeated periodically, suchas on an occasional or best effort basis (e.g., via a store and forwardnetwork) in order to verify that no control parameters have changed. Inthis regard, a change of location or situation of one or more sensorscould cause a system to prompt a user to perform a manual re-pair, orthe re-pairing process may be automatically performed in the background.

Where two or more sensors are in close proximity, parts of each tablemay be ring-fenced for each respective sensor. For example, each sensormay be assigned to a range of possible frequencies on the even table, orto a range of possible frequencies on the odd table. Additionally, theremay be a switch, or some other type of input, on a sensor to define apreferred behaviour. For example, the switch may be set to adjust whichfrequency the sensor will operate at, or to select whether the sensorwill operate at frequencies of the even table or the frequencies of theodd table or some portion thereof.

It also may be desirable that other metrics of the RF environment becollected by one or more sensor devices of the system. For example,other metrics of the RF environment which may be collected could be thespacing or a measure of distance between the sensors and the relativeorientation of the sensors. Using these metrics, a configuration may beprogrammed such that the sensors cooperate in order to minimise mutualinterference. Should the sensors be placed in a position where anelevated level of residual interference is likely, before or after apairing routine is performed, the sensors may provide a notification toreposition or re-orient one or more of the sensors.

4.4 Detection of Friend or Foe

As noted, there are cases where multiple sensors, such as two or more,are in proximity and can interfere strongly with each other ifcountermeasures are not taken. However, even though the sensors caninterfere, they are “friends” in that they can be configured to havespecific behaviours when detecting and adjusting to interference fromeach other. In contrast, third party sources of RF signals may interferewith the operation of a sensor by accidentally or actively jamming thepulse sequences. Such third party sources operating at a similar centrefrequency to a sensor may be considered “foes”; examples could be asensing technology from another manufacturer or supplier operating at asimilar frequency/pulsing strategy, or perhaps a malicious user tryingto deliberately disrupt the operation of a medical cardiorespiratorysensor. Other exemplar sources that could interfere may be anin-bedroom/in-hospital (or outside bedroom) combined passive infraredsensor (PIR) and microwave security detector (e.g., where the microwavedetector component operates at a similar RF centre frequency), a highpower aviation RADAR, and/or a military, police or traffic management orvehicular RADAR may all produce similar centre frequencies which couldinterfere with operation of a sensor.

For the case of interference caused by friendly sensors, the sensors maybe programmed to deliberately scan a frequency range to determine thepresence of interference. In that regard, one or more of the friendlysensors may each modify its centre frequency, in a search mode toattempt to maximise interference. Upon maximising interference, thesensors may then reconfigure their centre frequency to minimiseinterference. A frequency range between the maximised and minimuminterference frequencies may then be determined by the sensor(s). Thesensors may then determine if the frequency range is related to, forexample, a known frequency range, and if so, the sensors may assume thatanother sensor of a known type is the source of the interference. Suchscanning would preferentially occur during the absence of any motion inthe vicinity of the sensors.

Based on the determination that a friendly sensor is the source ofinterference, the sensors may initiate communication (e.g., usingManchester coding). For example, one or more of the sensors may adjusttheir respective centre frequencies around a determined interferencemaximum until two or more sensors agree upon the maxima. In this regard,a first sensor may move its centre frequency at a predefined rate, withthe second (or plurality of other sensors) detecting when aninterference maxima is achieved. Each sensor could communicate an agreedupon maxima point, and then agree which sensor should move to seek aminima frequency point. Upon achieving the minima, the sensor whichadjusted to the minima would hold at that centre frequency until acorrection is needed, for example, to account for temperature drift orother changing factor.

Such cooperative actions between friendly sensors may be made throughbase stations, and/or through mesh network of devices. In that regard,sensors may be reconfigurable, e.g., have the ability to dynamicallyadjust centre frequency by, for example, including a processor thatcontrols varying voltage to a voltage controlled oscillator for example,and/or other RF characteristics including pulse timing and radiatedpower. In another embodiment, coding may be applied to some RF pulsetrains to enable faster communication between “friends” without usingother communications channels.

Therefore communication of a polling event to local or remote processorusing a control signal is enabled in order to account for briefinterfering signal and mask out. As such, this realises a system with nointer-communication needed (i.e., exact knowledge of current centrefrequency is not needed). Thus, a temperature variation reference, e.g.,detection of a certain temperature change, may be used to trigger orinitiate polling between the sensors for updating the frequencies ofeach sensor to avoid interference as a result of recent temperaturechanges.

Based on the maximum interference detected and a sensor's own centrefrequency, it is possible to measure the frequency of the interferencesignal. How this works is by (a) knowing the centre frequency of thesensor, (b) optionally sweeping the centre frequency, (c) locatingmaximal interference, and (d) deducing the frequency of this interferingsource. Where maximal (or high/elevated) interference is detected, itcan be deduced that the interfering source has a component at thatfrequency. Once the interfering frequency is known, it is possible toreconfigure the sensor, alert the user, or indeed reconfigure the thirdparty interfering source (e.g., for the case where configuration of thethird party sensor(s) is possible, such as by turning off, adjustingangle, distance, frequency, power level etc.). Maximal interference isdefined by maximal noise; this can be measured by looking at the higherfrequency components in the baseband or intermediate frequency. For theexample of a sensor with baseband range from DC to 200 Hz, andintermediate frequency of 8 kHz, a filter range to check forinterference could be say 500-1500 Hz (roughly, they are factors of 10apart; one centred around the 100, one around the 1000, oneapproximately around the 10,000) (see FIG. 15). FIG. 16A shows exemplarin-phase and quadrature (IQ) baseband signals in the time domain with nointerference. FIG. 16B shows an intermittent interfering signal, which16C shows to have peak noise greater than 200 mVrms and unpredictable ofthe peak noise level.

4.5 Adjustment of Centre Frequency to Avoid Foes (or Other InterferingSources)

As previously described, strong interference sources which are not fromother sensors (i.e., friends), may be considered foes. A foe maytransmit a RF signal with a centre frequency close or identical to thefrequencies being transmitted by the one or more sensors. Accordingly,it is desirable for sensors to be able to operate in the presence offoes which may transmit jamming signals or other malicious RF emissions.

In some embodiments, the continued detection of an RF interference,caused by a foe, by a sensor cooperating with another sensor or sensors,may prompt a system to adjust the frequencies within which it isoperating. For example, the system may carry out a search across anallowable lookup table of values or other allowable blocks of radiospectrum in order to find a situation such that the unusual externalinterference is minimised. If the third party source was a sensor usinga similar pulsing scheme, it can be seen that moving to a nullinterference frequency (e.g., moving centre frequency by 125 kHz mightbe sufficient to minimise interference, and/or by adjusting PRF). Ifthis was unsuccessful, it can be seen that a sensor could adjust centrefrequency in steps in order to build up a picture of the local RFenvironment, and carry out an optimization process (e.g., using gradientdescent interference avoidance) in order to locate an interferenceminima over time. In some examples, this may require a large change incentre frequency, such as, for example, a move from 10.587 GHz to 9.3GHz (or vice versa).

Should the system be unsuccessful in minimizing the externalinterference caused by foes and/or other sources, the system may informa user. For example, the system may attempt to adjust operation viaclocking, transmission of adjusted centre frequencies or centretraversal via a special lookup table. If such adjustments areunsuccessful, the system may inform the user that a readjustment is“Unsuccessful,” as residual interference detected is such that itexceeds a predefined acceptable threshold. Optionally, such informationcan be presented to the user only if the interference is sustained innature. In certain extreme cases of interference, the sensor's RF radiomay be turned off automatically, and an error signal set (e.g.,displayed on a screen). As such, the sensor may be unable to processand/or extract physiological signals, and thus unable to detect user'sbiometric parameters. Further, if detected, the biometric parameters maybe inaccurate.

5. Noise Reduction without a Synchronization Requirement

In some embodiments, noise reduction may be achieved withoutsynchronization between two or more sensors. In that regard, the sensorsmay be configured to minimize RF coexistence issues withoutsynchronizing the frequency or timing of the sensors.

5.1 Reduce RF Pulse Width

One such technique may include reducing the RF pulse width to lessen theprobability of interference. Turning back to FIG. 5A, pulse width r maybe used to determine the length of the RF pulse signals. Reduction ofthe pulse width while maintaining the pulse repetition interval, PRI,may have no adverse effect on the sensor operation. Additionally, theshorter pulse width has less chance of being modulated with other pulsesthan do longer pulses. The lowest pulse width value may be chosen tomeet regulatory approval standards requirements for the RF signalbandwidth and spurious signal level.

5.2 Dither Each Sensor

Another technique for noise reduction may include dithering the pulsetiming of each sensor differently or maintaining the pulse timing ofeach sensor at a constant frequency offset to each other. In thisregard, the different timing from a master and slave sensor could reducethe chance of the sensors RF pulses locking in-phase with each other.

5.3 Increase Dither Timing

The pulse timing dither between two sensors may also be increased andmade pseudo random to reduce noise. Similar to dithering the time ofeach sensor, the dithering cycle could be extended and made pseudorandomfor either, or both, the master and slave sensor. In some examples, asecond binary ripple counter and exclusive OR gate, or a microcontrolleror processor may be used to create the extended and pseudorandomdithering cycle. As stated already, the synchronous nature of thedithering or pseudo random timing dithering with the PRF (and IF) issignificant so that tone artefacts are not produced by the phasesensitive demodulator receiver of the sensor. In one example, a diodemay be coupled with a timing oscillator (e.g., pulse generator 408 ofFIG. 4) configured to control emission of timed pulses from the DRO. Thevoltage level on the diode may be ramped up, thereby changing the diodecapacitance. This leads to a change in the frequency of oscillation ofthe timing oscillator. As such, timing dithering may occur.

5.4 Dither the RF Frequency

Another technique for asynchronously reducing the noise and interferenceis to dither the dielectric resonant oscillator (DRO) RF frequency tomitigate PRF frequency locking. Further, frequency dithering has theadvantage of mitigating external RF interference. In some examples, anadditional circuit to either modulate the drain voltage of the DRO ordither the supply voltage of the DRO from a voltage controlled regulatormay be required. In this regard, by ramping the supply voltage of theDRO, the frequency output by the DRO may be adjusted.

Frequency dithering may allow for multiple sensors to coexist in acommon vicinity. For example, by employing frequency dithering, thecenter frequency of each sensor is moving such that there is astatistically insignificant chance that interference occurs between thesensors in normal operation. Such a technique may also be utilized byitself or in addition to timing dithering.

5.5 Single Housing

Another technique for reducing noise between sensors is by positioningthe sensors in a single housing unit. As shown in FIG. 14, two sensors1406 and 1408 are placed within housing unit 1400. Sensor 1406 is placed180 degrees away from sensor 1408, and accordingly signals 1402 and 1404create minimal, if any, interference. Turning back to FIG. 9, the lowestlevel of noise between sensors occurs when the sensors are placed atleast 90 degrees apart. Accordingly, when placing the sensors within thehousing, they should be at an angle of at least 90 degrees from eachother. A benefit of this technique is the sensors can be easilysynchronized through a direct connection.

5.6 Orientation

Because the signal level of the interference source is important thelocation of the sensors has a role to play in reducing noise. Placingsensors in close proximity and in a line of sight of each other producesmaximum interference noise. This noise can be mitigated by orienting thesensors to increase the effective path length. Locating sensors furtherapart and at an angle to each other is an effective means of reducingcoexistence noise

5.7 Polarisation

When the sensors transmit and receive RF signals are circularlypolarised (i.e., their RF signal electric and magnetic fields have apreferred transmit and receive direction) then further noise reductioncan be achieved by arranging the sensors such that the polarisation ofone sensor is orthogonal to that of the other. In this way the reflectedmovement signal is preferred (suffers no attenuation due topolarisation) while the received interference RF signal is rejected(suffers attenuation due to its orthogonal polarisation).

6. Combination Configurations

Noise reduction may also be obtained by using more than one of thepreviously described noise reduction architectures and/or techniques. InTable 1 below: “S” represents Synchronization and “D” representsDithering. For the case of a term in brackets “Q”, this implies the caseof “S” and/or “D” (i.e., to simplify the presentation of Table 1). ForTable 1, “t” represents Timing (which includes IF timing and PRFtiming). “f” represents the RF centre frequency. “nothing” representswhere no intervention is made (i.e., noting/nothing is the trivial as-iscase). Table shows the case of 1 co-existing sensor, but could beextended to (1, 2, . . . n) linked sensors. It should be noted thatsynchronization of timing implies the synchronization of a wired orwireless control signal (i.e., a first control signal); if dithering isalso employed (simultaneous synchronization of timing and the ditheringof timing), then a second control signal is used to facilitatesynchronization. For timing synchronization, this implies that the PRFtiming are locked. For dithering, this implies that IF and PRF aresynchronised, but dithered (hence the requirement for the second controlsignal).

A potential limitation of timing synchronization alone is that itrequires good RF pulse isolation. (RF bleed through of the RF signalduring the OFF period of the RF modulation results in poor RF pulseisolation). Therefore, it is desirable to turn off the RF radiotransmitter between pulses or other approaches to remove this bleedthrough.

In considering Table 1, the combination of timing dither and frequencysynchronization [t(D) f(S)] is likely to perform well. The combinationof timing synchronization and frequency synchronization [t(S) f(S)] isalso likely to perform well, especially if there is good isolation, ortiming synchronization and timing dither and frequency synchronization[t(S,D) f(S)].

TABLE 1 t (of IF and PRF) f Nothing Nothing S (D) Nothing S (D) DNothing S D S S (D) S D D D Nothing Nothing D

7. Other Considerations 7.1 Correcting for Temperature Variation

A centre frequency of a sensor may shift, even under the control of aDRO, as certain operating parameters change. In this regard, a variationin both ambient and internal temperature may cause a sensor's frequencyoutput to shift. In some examples, sensors may experience repeated andsignificant changes in temperature if a high power light or heat sourceis in proximity of, or in the same housing as, an RF sensor, and such asource switches on or off over time. There may also be a shift in centrefrequency when a product with a processor and sensor is first turned on,and the enclosure reaches the expected operating temperature of thesystem (which may be above ambient temperature).

For the case of a system that contains separate temperature monitoring,a detection of a change in temperature (with reference to rate of changein temperature over time) can be used to adjust the sensor transmissionfrequency. Therefore, embodiments may include design parameters toassist the sensor in outputting a certain frequency, regardless of anytemperature variations.

For a system with two or more sensors sending a continuous clock orassociated reset synchronization signal over wired or wireless link withdefined QoS, any temperature or related change in centre frequency mayautomatically be corrected. In this regard, the sensors may be adjustedby the techniques previously described regarding QoS.

For a system with two or more sensors sending periodic centre frequencyvalues read from sensors, optimal spacing may be maintained. Forexample, the sensors may transmit the values read from the sensors overa network, which allows the adjustment of one or more sensors in such away that defined frequency spacing is achieved and retained. As such,interference between sensors may be minimized. Such corrections may bemade based on a change or delta in a centre frequency of a sensor abovea defined threshold.

For a system with two or more sensors using lookup tables, subsequent toan initial pairing process, each sensor may be able to dynamicallydetect their current centre frequency (e.g., as drifting due to a changein temperature or other parameter), and continually or on a periodicbasis adjust its frequency in order that it matches an agreed lookuptable centre frequency. Such adjustments may thereby minimisinginterference between the sensors, while assuring the sensors remainwithin a defined spectral mask.

RF sensor variation and processor control offsets may also be used toestimate the temperature such that an RF sensor alone could be used toestimate temperature to a certain resolution. In this regard, thetemperatures may allow for sensor start-up effects, and further, theresolution may enable temperature sensing where no separate temperaturesensor is provisioned. Accordingly, no prior knowledge of a temperaturecoefficient of the oscillator may be necessary.

7.2 Reduce Sensor Synchronization Events

The amount of times a sensor may provide its actual centre frequency tonearby sensors may be reduced by reading and accurately setting thecentre frequency at the time of manufacture. In this regard, it ispossible to know the maximum and minimum extremes, in terms oftemperature, with which a DRO or a quartz crystal operates. Based on themaximum and minimum extremes, it is also possible to determine atemperature coefficient, as operation of the DRO may be linear. Based onthe frequency of operation being output by the sensor, an adjustment tocorrect for inaccuracies caused by the operating temperature may be madegiven the known temperature coefficient.

7.3 Third Party Timing Correction

In embodiments where a sensor measures its own centre frequency, theaccuracy of the clock producing the RF signals may be known and adjustedfor in the centre frequency determination. For example, a network timeprotocol (NTP) may be used to determine the actual frequency of theclock at a certain time. A timing calibration may then be performed onthe clock, so the other sensors may be adjusted to assure they operateat previously defined differences in frequency. NTP is a networkingprotocol for clock synchronization between systems over packet-switched,variable-latency data networks (e.g., the internet, and using UserDatagram Protocol (UDP) on port number 123).

Commercial crystals may have a known clock rate and accuracy. Forexample, a crystal may have an accuracy of 20 parts per million, and anassociated variation with temperature. In cases of a slow temperaturechange, for example, a period of 10 or 30 mins, a timing calibration canbe performed on the 4 MHz clock. In this regard, once the current timeis available, it is possible to send to the other devices.

To provide the current time to other sensors, the clock rate, in thisexample a 4 MHz clock, may be mixed with a frequency rate, for example10.525 GIL. As a result of the mixed signal, a harmonic of the 4 MHzclock signal appears on the received signal. Therefore, based on theoutput, there is a frequency that is:

n*actual frequency

Where n is an integer and where actual frequency is the outputtedfrequency of the sensor (in the current example 10.525 GHz). The clockrate, due to accuracy issues, may be slightly different than theadvertised rate. Continuing the above example, the clock rate may be4.01387 MHz. To assure an accurate timing between the sensors, the clockrate may be adjusted until the output frequency includes no frequencydeviation and/or beat frequency. Based on the adjusted rate, the crystalcan be determined to be operating at n times the clock rate.

Based on the passage of time using the network timing protocol or GPStiming signals or other time reference, a clock synchronization signalmay be calculated. For example, a reference frequency may be found froman internet source. Based on passage of time using the NTP, a clocksynchronization signal may be calculated. This synchronization signalmay then be sent to the other sensors.

7.4 Location Aware Sensor Parameters

In some embodiments it may be possible for a sensor to obtain locationinformation. In this regard, the sensor may include or have access tothe data of a positioning system, such as a global positioning system(GPS), whereby the sensor may obtain geographical location informationas to where the sensor is currently positioned. In some embodiments, thesensor may be included in, or connected to, a smart-device (e.g.,smartphone, tablet, smartwatch etc.). Accordingly, the sensor mayreceive its geographical location information from that smart-device.Timing information may also be recovered via a GPS receiver, and couldallow wireless synchronization (assuming that an adequate GPS signal isavailable).

Based on input of geographical location information, the sensor may thenassure that its operation is within an allowed spectral mask for thecurrent geographical region which the sensor is located. Alternatively,the sensor may automatically deactivate if possible control set ofparameters of the sensor are incapable of operating the sensor withinthe allowed spectral mask of the geographical region which the sensor islocated. Therefore, one or more sensors can coexist both with localradio frequency regulations and with one another.

7.5 Low Power State

Sensors may be switched to a low power search mode (or even a sleep oroff mode) if no motion is detected for a predetermined amount of time.In this regard, a sensor might be integrated into body worn devices,such as pendants, chest bands, bracelets, watches, hats, and other suchdevices. Additionally, sensors may be directly into existing electronicsdevices such as, smart watches, smartphones, internet of things (IoT)devices, etc.

As such, sensors may be programmed to switch to a low power search modeif the device which the sensor is integrated is not being used, such asif no motion is detected. For example, a sensor integrated into apendant may be placed onto a dresser. Since the user is not wearing thependant, the sensor may detect no motion. Accordingly, the range of thesensor may be adjusted by reducing the output power, frequency, and/orduration of pulses to reduce the overall power consumption. Further, theadjustments may be programmed to be within allowable ranges. Whilesensors integrated into devices are described, standalone sensors mayalso be programmed to switch to a lower power search mode if the sensorfails to detect motion. Therefore, a low power condition can act afurther aid to coexistence, by reducing the RF emitted power of one ormore sensors.

7.6 Security

Sensors might also be used in security sensing applications, to detectunauthorised physiological patterns (e.g., intrusion of a person orpersons) into a detection area, and raise an alarm (or send a controlsignal to processor). As can be seen, in a security application, manysuch sensors could be co-located in a building, and thus RF sensorcoexistence is highly important. It is also possible that one or moresleep sensors could be reconfigured by a control system when the user isaway during the day to act as nodes or sensors in an intruder (burglar)alarm system (e.g., to detect an intruder in a bedroom).

7.7 Processing

Processing of signals, such as those received by a sensor, may beperformed by a processor on a sensor printed circuit board assembly(PCBA). Such a PCBA may also allow communication over an analog and/ordigital link with a remote processor, such as a microprocessor on a mainboard.

In embodiments with digital sensors, signals may be digitized andtransmitted over a wireless or wired connection. Digitisation may beperformed at a high resolution and/or sampling rate, and the sensorsignals themselves (e.g., in-phase (I) and quadrature (Q) streams, or astream prior to or not requiring such separation of I and Q), may betransmitted to a single or multiple processors. Further, each channel oftransmitted information may also contain information about current orrecent centre frequency, relative changes in centre frequency, lookuptable location in use, etc.

The number of components to implement a multi-sensor system may bereduced by minimising component count on one or more sensors. Forexample, in an operating environment, such as a home, apartment block,hotel, office, hospital or nursing home where multiple sensors are inuse, the system may utilise existing data links and/or data processingpower available in a wider system implementation in order to achieve thedesired motion and physiological sensing. In one example, sensors maytransmit their respective signals to a remotely located, separatelyhoused processor, capable of processing multiple sensor signals at once.

Optionally, digitised sensor signals could be transcoded to audiofrequencies such that existing audio processing accelerators androutines might be utilised in order to detect specific motion patterns.

In addition, whilst the main focus of the described technology isassociated with applications for detecting respiration, sleep and heartrate, it is similarly suitable for detecting other movements of thehuman body (or of an animal if so configured).

Unless the context clearly dictates otherwise and where a range ofvalues is provided, it is understood that each intervening value, to thetenth of the unit of the lower limit, between the upper and lower limitof that range, and any other stated or intervening value in that statedrange is encompassed within the technology. The upper and lower limitsof these intervening ranges, which may be independently included in theintervening ranges, are also encompassed within the technology, subjectto any specifically excluded limit in the stated range. Where the statedrange includes one or both of the limits, ranges excluding either orboth of those included limits are also included in the technology.

Furthermore, where a value or values are stated herein as beingimplemented as part of the technology, it is understood that such valuesmay be approximated, unless otherwise stated, and such values may beutilized to any suitable significant digit to the extent that apractical technical implementation may permit or require it.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this technology belongs. Although any methods andmaterials similar or equivalent to those described herein can also beused in the practice or testing of the present technology, a limitednumber of the exemplary methods and materials are described herein.

When a particular material is identified as being preferably used toconstruct a component, obvious alternative materials with similarproperties may be used as a substitute. Furthermore, unless specified tothe contrary, any and all components herein described are understood tobe capable of being manufactured and, as such, may be manufacturedtogether or separately.

It must be noted that as used herein and in the appended claims, thesingular forms “a”, “an”, and “the” include their plural equivalents,unless the context clearly dictates otherwise.

All publications mentioned herein are incorporated by reference todisclose and describe the methods and/or materials which are the subjectof those publications. The publications discussed herein are providedsolely for their disclosure prior to the filing date of the presentapplication. Nothing herein is to be construed as an admission that thepresent technology is not entitled to antedate such publication byvirtue of prior invention. Further, the dates of publication providedmay be different from the actual publication dates, which may need to beindependently confirmed.

Moreover, in interpreting the disclosure, all terms should beinterpreted in the broadest reasonable manner consistent with thecontext. In particular, the terms “comprises” and “comprising” should beinterpreted as referring to elements, components, or steps in anon-exclusive manner, indicating that the referenced elements,components, or steps may be present, or utilized, or combined with otherelements, components, or steps that are not expressly referenced.

The subject headings used in the detailed description are included onlyfor the ease of reference of the reader and should not be used to limitthe subject matter found throughout the disclosure or the claims. Thesubject headings should not be used in construing the scope of theclaims or the claim limitations.

Although the technology herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thetechnology. In some instances, the terminology and symbols may implyspecific details that are not required to practice the technology. Forexample, although the terms “first” and “second” may be used, unlessotherwise specified, they are not intended to indicate any order but maybe utilised to distinguish between distinct elements. Furthermore,although process steps in the methodologies may be described orillustrated in an order, such an ordering is not required. Those skilledin the art will recognize that such ordering may be modified and/oraspects thereof may be conducted concurrently or even synchronously.

It is therefore to be understood that numerous modifications may be madeto the illustrative embodiments and that other arrangements may bedevised without departing from the spirit and scope of the technology.It will further be understood that any reference herein to subjectmatter known in the field does not, unless the contrary indicationappears, constitute an admission that such subject matter is commonlyknown by those skilled in the art to which the present technologyrelates.

PARTS LIST

-   detection apparatus 100-   detection apparatus 102-   sensor 300-   sensor 302-   RF pulse 310-   RF pulse 312-   sensor 402-   oscillator 404-   pulse generator 408-   periodic sinusoidal amplitude envelope 600-   signal 602-   signal 700-   signal 702-   resultant receiver RF signal 704-   sensor 800-   second active source 802-   object 804-   rf signal 806-   signal 808-   master sensor 1201-   slave sensor 1202-   red signal 1204-   master sensor circuit 1301-   slave sensor circuit 1302-   housing unit 1400-   signal 1402-   signal 1404-   sensor 1406-   sensor 1408

1. A radio frequency motion sensor configured for operation in amulti-sensor configuration, the radio frequency motion sensorcomprising: a radio frequency transmitter, the transmitter configured toemit pulsed radio frequency signals; and a receiver configured toreceive reflected ones of the emitted pulsed radio frequency signals todetect motion of a reflecting surface; wherein the transmitter isconfigured for synchronized transmission of the pulsed radio frequencysignals with another radio frequency motion sensor in a vicinity of theradio frequency motion sensor to mitigate interference between emittedpulses from the radio frequency motion sensors.
 2. The radio frequencymotion sensor of claim 1 wherein the transmitter is synchronized in timeto interleave emitted pulsed radio frequency signals with emitted pulsedradio frequency signals of the another radio frequency motion sensor. 3.The radio frequency motion sensor of claim 2 wherein synchronizationbetween the radio frequency motion sensors comprises transmission of aclock signal.
 4. The radio frequency motion sensor of claim 3 whereinthe synchronization between the radio frequency motion sensors comprisestransmission of a dither synchronous signal.
 5. The radio frequencymotion sensor of any one of claims 3 to 4 wherein the radio frequencymotion sensor detects timing from an emitted pulsed radio frequencysignal.
 6. The radio frequency motion sensor of any one of claims 3 to 4wherein the radio frequency motion sensor detects a synchronizationsignal independent of the emitted pulsed radio frequency signals.
 7. Theradio frequency motion sensor of any one of claims 1 to 4 wherein theradio frequency motion sensor further comprises an infra-red signaltransmitter adapted for timing of the emitted pulsed radio frequencysignals.
 8. The radio frequency motion sensor of any one of claims 1 to4 wherein the radio frequency motion sensor comprises an interface forwired connection with the another radio frequency motion sensor, thewired connection being configured for timing of the emitted pulsed radiofrequency signals.
 9. The radio frequency motion sensor of claim 1wherein the transmitter is synchronized with a transmitter of theanother radio frequency motion sensor with respect to frequency toreduce interference.
 10. The radio frequency motion sensor of claim 1wherein the transmitter comprises a variable oscillator configured forfrequency adjustment in response to detected interference noise.
 11. Theradio frequency motion sensor of any one of claims 1 to 10, wherein thetransmitter is further configured for frequency dithering.
 12. The radiofrequency motion sensor of any one of claims 1 to 11, wherein thetransmitter is further configured for time dithering.
 13. A radiofrequency motion sensor, the radio frequency motion sensor comprising: aradio frequency transmitter, the transmitter configured to emit pulsedradio frequency signals; and a receiver configured to receive reflectedones of the emitted pulsed radio frequency signals to detect motion of areflecting surface; wherein the transmitter is configured with a dithertiming different from a dither timing of another radio frequency motionsensor in a vicinity of the radio frequency motion sensor to mitigateinterference between emitted pulses from the radio frequency motionsensors.
 14. The radio frequency motion sensor of any one of claims 11,12 and 13, wherein the dither timing of the transmitter is pseudorandom.
 15. The radio frequency motion sensor of any one of claims 13 to14 wherein the transmitter is configured with frequency dithering.
 16. Aradio frequency motion sensing apparatus comprising: two or more radiofrequency sensors, each sensor comprising a radio frequency transmitterconfigured to emit pulsed radio frequency signals; and a receiverconfigured to receive reflected ones of the emitted pulsed radiofrequency signals to detect motion; wherein the apparatus comprises ahousing to maintain the sensors in a configuration to emit the radiofrequency signals in different directions to mitigate interferencebetween emitted pulses from the radio frequency sensors.
 17. The radiofrequency motion sensing apparatus of claim 11 wherein sensors arepositioned to direct the emitted pulses at a relative angle of about 90degrees to 270 degrees.
 18. The radio frequency motion sensing apparatusof claim 16 or claim 17, wherein the sensors are positioned to directthe emitted pulses at a relative angle of about 180 degrees or greater.19. A system for transmitting radio frequencies comprising: a masterradio frequency motion sensor; and a slave radio frequency motionsensor; wherein the master radio frequency motion sensor is configuredto transmit a first radio frequency (RF) signal; and the slave radiofrequency motion sensor is configured to transmit a second RF signal,wherein the system is arranged to minimise interference between thefirst radio frequency (RF) signal and the second RF signal.
 20. Thesystem of claim 19, wherein the slave radio frequency motion sensor isconfigured to transmit the second RF signal such that the second RFsignal creates minimal interference with the first radio frequency (RF)signal.
 21. The system of claim 19 or claim 20, wherein the master radiofrequency motion sensor and slave radio frequency motion sensor areplaced within a single housing.
 22. The system of claim 21, wherein themaster radio frequency motion sensor and slave radio frequency motionsensor are positioned within the single housing at an angle of 90degrees.
 23. The system of any one of claims 19 to 22, wherein an RFtransmitter is configured to transmit at least one synchronization RFpulse signal.
 24. The system of claim 23, wherein the slave radiofrequency motion sensor is further configured to receive thesynchronization RF pulse signal.
 25. The system of claim 24, wherein theslave radio frequency motion sensor is further configured to detect thereceived synchronization RF pulse signal at an intermediate frequency.26. The system of claim 23, wherein the master radio frequency motionsensor is further configured to transmit the at least one RF pulsesignal on a separate industrial, scientific and/or medical transmissionband (ISM).
 27. The system of any one of claims 19 to 22, wherein: themaster radio frequency motion sensor further comprises an infra-red (IR)transmitter configured to transmit an IR synchronization signal; and theslave radio frequency motion sensor further comprises an infra-red (IR)receiver configured to receive the transmitted IR synchronizationsignal.
 28. The system of any one of claims 19 to 22, wherein the masterradio frequency motion sensor and the slave radio frequency motionsensor further comprise a master-slave oscillator circuit.
 29. Thesystem of claim 28, wherein the master-slave oscillator circuit furthercomprises a multi-wire cable interconnection configured to transmittiming and dithering synchronization information from the master radiofrequency motion sensor to the slave radio frequency motion sensor. 30.The system of any one of claims 19 to 22, wherein at least one of themaster radio frequency motion sensor and the slave radio frequencymotion sensor includes at least one resonator oscillator circuit. 31.The system of claim 30, wherein at least one resonator oscillatorcircuit includes a quartz crystal.
 32. The system of claim 30, whereinthe slave radio frequency motion sensor includes the at least oneresonator oscillator circuit as well as a voltage controlled RFoscillator, wherein the voltage controlled RF oscillator is configuredto synchronize its RF signal frequency to the master radio frequencymotion sensor.
 33. The system of claim 32, wherein the voltagecontrolled RE oscillator is configured to synchronize the RF frequencyto the master radio frequency motion sensor by detecting a high voltagewhich result in a high level of interfering noise, detecting a lowvoltage which result in a high level of interfering noise and moving thevoltage controlled RF oscillator to a central control voltage positionbetween the high and low voltage.
 34. The system of any one of claims 19to 33, wherein at least one of the first radio frequency (RF) signal andsecond RF signal has an RF pulse width of about 0.5 μs.
 35. The systemof any one of claims 19 to 34, wherein the master radio frequency motionsensor is configured to provide a first dithering time to the firstradio frequency (RF) signal; and the slave radio frequency motion sensoris further configured to provide a different dithering time to thesecond RF signal.
 36. The system of any one of claims 19 to 35, whereinthe master radio frequency motion sensor includes a first binary ripplecounter and exclusive OR gate; and the slave radio frequency motionsensor includes a second binary ripple counter and exclusive OR gate;wherein, the first and second binary ripple counter and exclusive ORgates are configured to create a pseudo random dithering time.
 37. Thesystem of any one of claims 19 to 36, wherein the master radio frequencymotion sensor includes a first dielectric resonant oscillator, whereinthe first dielectric resonant oscillator is modulated by a firstvoltage; and the slave radio frequency motion sensor includes a seconddielectric resonant oscillator, wherein the second dielectric resonantoscillator is modulated by a second voltage.
 38. The system of any oneof claims 19 to 37, wherein the first radio frequency (RF) signal andsecond RF signal are at different frequencies.
 39. The radio frequencymotion sensor of claim 1 wherein the transmitter is configured to ditherthe frequency of the pulsed radio frequency signals.
 40. A system fortransmitting radio frequencies comprising: a first radio frequencymotion sensor; and a second radio frequency motion sensor; wherein thefirst radio frequency motion sensor is configured to transmit a firstradio frequency (RF) signal; and the second radio frequency motionsensor is configured to transmit a second RF signal, wherein the systemis arranged to minimise interference between the RF signals of bothsensors.
 41. The system of claim 40, wherein the first radio frequencymotion sensor is configured to receive an indication of the frequencytransmitted from the second radio frequency motion sensor, and thesecond radio frequency motion sensor is configured to receive anindication of the frequency transmitted from the first radio frequencymotion sensor.
 42. The system of claim 41, wherein the first radiofrequency motion sensor is configured to adjust the frequency of thefirst radio frequency (RF) signal in response to the received indicationof the frequency transmitted from the second radio frequency motionsensor.
 43. The system of claim 40, wherein each of the first radiofrequency motion sensor and the second radio frequency motion sensor isconfigured to access a lookup table which includes selectablefrequencies at which the sensors can operate.
 44. The system of claim43, wherein the first radio frequency motion sensor is configured toselect a frequency from a first lookup table, and the second radiofrequency motion sensor is configured to select a frequency from asecond lookup table.
 45. The system of claim 44, wherein the firstlookup table comprises odd frequencies and the second lookup tablecomprises even frequencies.
 46. The system of claim 40, wherein thefirst radio frequency motion sensor and the second radio frequencymotion sensor are configured to adjust their respective frequenciesusing a network time protocol (NTP).
 47. The system of claim 40, whereinthe first radio frequency motion sensor and the second radio frequencymotion sensor are configured to adjust their respective transmissionfrequencies in response to detecting interference.
 48. The system ofclaim 40, wherein the first radio frequency motion sensor and the secondradio frequency motion sensor are configured to adjust their respectivetransmission frequencies based on predetermined temperaturecoefficients.
 49. The system of any one of claims 40 to 48, wherein thefirst radio frequency motion sensor and the second radio frequencymotion sensor are configured to check or adjust the frequency at whichthey transmit RF signals in response to input of geographical location.50. The system of any one of claims 40 to 49, wherein at least one ofthe first radio frequency motion sensor and the second radio frequencymotion sensor is configured to operate in a low power mode upondetection of an absence of motion.
 51. The system of claim 40, whereinthe first radio frequency motion sensor and the second radio frequencymotion sensor are configured to send a continuous clock signal over awired or wireless link.
 52. The system of claim 40, wherein at least oneof the first radio frequency motion sensor and the second radiofrequency motion sensor is configured to: send periodic centre frequencyvalues read from each respective sensor over a network; and adjust thefrequency at which each sensor transmits to minimise interferencebetween the first and second sensors.
 53. The system of claim 40, 43 or44, wherein at least one of the first radio frequency motion sensor andthe second radio frequency motion sensor is configured to: dynamicallydetect its respective current centre frequency; and periodically adjustsuch frequency in order that it matches an agreed lookup table centrefrequency so interference between the first and second radio frequencymotion sensors is minimized, while remaining within a defined spectralmask.
 54. The system of claim 40, 43, or 44, wherein the first radiofrequency motion sensor and the second radio frequency motion sensor areconfigured so that: a frequency range is dynamically scanned to detectminimum and maximum interference; and a centre frequency of at least oneof the sensors is adjusted to a frequency associated with the minimum.55. The system of claim 54 wherein the sensors communicate via afrequency of maximum interference.
 56. The system of claim 40, 43, or44, wherein at least one of the first radio frequency motion sensor andthe second radio frequency motion sensor is configured to: detect atemperature change; and initiate polling between the sensors, based onthe detected temperature change, for adjusting a centre frequency of atleast one of the sensors.
 57. The system of claim 40 wherein the systemis arranged to minimise interference between the RF signals of bothsensors by frequency dithering of one or more oscillators of the sensorsgenerating the RF signals.
 58. The system of claim 57 wherein a voltagelevel to at least one of the one or more oscillators is ramped toproduce the frequency dithering.
 59. The system of any one of claims 40,57 and 58 wherein the system is arranged to minimise interferencebetween the RF signals of both sensors by timing dithering of pulses ofthe RF signals of both of the sensors.
 60. The system of claim 59wherein a voltage level to a diode coupled with at least one of the oneor more oscillators is ramped to implement the timing dithering of atleast one of the sensors.
 61. The system of any one of claims 58 and 60wherein the at least one of the one or more oscillators is a dielectricresonant oscillator.